By Sanjeev Miglani and Krishna N. Das NEW DELHI (Reuters) -An Indian student was killed by shelling in the eastern Ukrainian city of Kharkiv on Tuesday, prompting New Delhi to step up demands for safe passage to evacuate thousands of its nationals trapped in the war zone. Invading Russian forces are trying to lay siege to Kharkiv, firing volleys of artillery that have killed civilians including children, Ukrainian officials say. Indian foreign ministry spokesman Arindam Bagchi said the ambassadors of Russia and Ukraine had been called in “to reiterate our demand for urgent safe passage for Ind…